The subject matter of this invention concerns a pneumatic positioning control unit for pneumatically controlling the position of a workpiece relative to a predetermined workpiece configuration.
Pneumatic position control units are known, there being, for example, a product manufactured by the firm of Samsomatic which is distributed as positioning controller Type 923-0010. This unit works on the basis of the dynamic pressure principle. The supply air flows at a constant preliminary pressure via a precision pressure regulator and a throttle valve through measuring nozzles which are built into a workpiece fixture. If correctly positioned, the workpiece shuts off the measuring nozzles. As a result, a dynamic pressure is generated between the measuring nozzles and the throttle valve. This pressure change is monitored by a pneumoelectric limit signal transmitter and displayed by means of a pressure gauge (analog display). As soon as the dynamic pressure reaches the set limiting value, a colored indicator light is turned off (digital display)xe2x80x94position okayxe2x80x94and the coordinated machine tool is turned on.
To avoid inaccuracies which can be caused, for example, by fluctuations of the supply pressure, another known positioning controller works on the basis of the differential pressure principle. This type of unit is distributed by the firm of Samsomatic as positioning controller Type 923-0013. In this case, the supply air flows at a constant preliminary pressure via a precision pressure regulator into a pressure divider and finally into a throttling device in the form of preliminary nozzles. The reference branch comprises a reference nozzle in which the sensitivity is set by means of an adjusting screw. In the measuring branch, the supply air flows through one or several measuring nozzles which are built into the workpiece fixture. If correctly positioned, the workpiece shuts off the measuring nozzles. As a result, a dynamic pressure is generated between the measuring nozzles and the preliminary nozzle. The pressure change is transformed by a piezoresistive pressure pickup into a proportional electric voltage signal which is applied to the electric analog display instrument via an electric measuring amplifier. The position is displayed by means of an indicator light which can light up in different colors.
In addition, there is a unit manufactured by the firm of Herion which pneumatically controls the position of a workpiece relative to a predetermined workpiece configuration in a workpiece fixture which comprises an enclosure base component and several modular enclosure components. When combined, the enclosure base component and the modular enclosure components form the overall enclosure. Each modular enclosure component is coordinated with a minimum of one measuring nozzle for a gaseous pressure medium in a contact surface of a workpiece fixture. Various modular enclosure components can be added to the overall unit, thus making it possible to include additional measuring nozzles to control the position in the workpiece fixture. The individual modular enclosure components are supplied by a supply air channel which leads from a pressure supply system inside the enclosure base component to the individual measuring nozzles. The measuring nozzles are coordinated with individual throttling devices as well as with a pressure sensor that is located downstream from the throttling device. As soon as the pressure falls below or exceeds a predetermined limiting value, the pressure sensor activates a signaling unit. The signaling unit is connected via signal lines to a central control unit. The limiting values for the individual pressure sensors are centrally set and transmitted via the signal lines to the signaling and/or display units (digital display).
As a result of the modular construction, it is easily possible to increase or to reduce the number of measuring nozzles and thus the number of measuring points depending on the requirements to be met in the workpiece fixture and on the shape of the workpiece.
The problem encountered, however, is that setting and displaying the limiting values and displaying the situation prevailing in the measuring nozzle is possible only by way of the central control unit and the two light-emitting diodes that display the minimum and the maximum value, respectively (digital display). The operating point in mid-position between the two limiting value""s can be accurately set only by way of a complicated feedback system between the machine tool for the workpiece and a centrally located control unit, provided that it has an analog display.
In addition, there is a pneumatic positioning control unit manufactured by the firm of Saia which comprises light-emitting diodes that display the minimum and maximum limiting values (digital display). It is, however, not possible to monitor the precise mid-position of the operating point since the unit does not have an analog display.
Thus, the problem to be solved by this invention is to design a unit for pneumatically controlling the position, in particular of a workpiece, by means of which the drawbacks mentioned above are eliminated, which has a simple and versatile design, and which makes it possible to locally set and display the values.
According to the invention, a unit for pneumatically controlling the position of an object, in particular of a workpiece, relative to a predetermined workpiece configuration comprises an enclosure with a minimum of one measuring nozzle for a gaseous pressure medium, which measuring nozzle is located in a contact surface of a workpiece fixture, a common pressure supply unit connected to the nozzle by way of pressure lines, separate adjoining modular enclosure components detachably connected to one another, each fitted with a connection leading to the measuring nozzle, a first enclosure end cover which can be connected to the pressure supply unit and a second enclosure end cover that is located at a distance from the first enclosure end cover, the first enclosure end cover, the modular enclosure components that adjoin the first enclosure end cover, and the second enclosure end cover that adjoins the modular enclosure components forming the overall enclosure, at least the first enclosure end cover and the modular enclosure components being connected to one another by way of pressure lines, each modular enclosure component being fitted with a display unit for the analog display of a pressure value measured by a pressure sensor, and each modular enclosure component comprising one throttling device that is coordinated with the nozzle, and with a differential pressure sensor which is located downstream from the throttling device and which actuates a signaling unit and/or the coordinated display unit as soon as the pressure falls below or exceeds a predetermined pressure limiting value.
In this manner, a simple design is ensured, and the actual pressure value can be displayed directly on the modular enclosure component at any given time. In addition, it is possible to locally display the set pressure limiting values as well as the pressure as it reaches or exceeds its preset limiting values. This type of design is particularly suitable in cases in which extensive production lines with sophisticated machining centers are involved since it eliminates the need for a complicated feedback system from the central controller during the setting or monitoring of the unit.
To make it possible to set the pressure limiting values separately for the nozzles that are coordinated with the modular enclosure components, the modular enclosure components are fitted with suitable means.
According to one particular embodiment of this invention, the display on the modular enclosure component is designed in the form of an LED display. The pressure value in the LED display is shown in the section of the LED display that lights up.
As an alternative or as an added feature, the display unit comprises at least a multi-digit digital display which displays the pressure value measured by the pressure sensor and/or a quantity that is assigned to the pressure value, such as the distance of the workpiece from the nozzle. By means of the digital display, it is possible to adjust and monitor the function of the unit more accurately. For example, a master workpiece is accurately placed into the workpiece fixture. The digital display displays a specific reference value which is subsequently stored. After a certain operating time, the master workpiece is again accurately placed into the workpiece fixture. If the digital display at this time displays a different value, the unit must be reset or replaced. In this manner, it is possible to monitor the function of the unit simply and more accurately since the digital display is able to display a greater resolution and thus a more accurate pressure value. The placement of the workpiece at a local point is important because it also makes it possible to ensure that it has been properly placed, thus eliminating the possibility of differing results due to erroneous placement.
To avoid inaccuracies as a result of pressure fluctuations in the gaseous medium, for example, the unit for detecting the pressure change in the nozzle is designed on the basis of the differential pressure principle. An air discharge line for exhausting the air discharged from the reference nozzle that is coordinated with the nozzle is provided in a modular enclosure component; this air discharge line connects the separate modular enclosure components and at least the second enclosure end cover with one another, and the second enclosure end cover is fitted with an air discharge opening, preferably with a sound absorber.
Alternatively, the unit for detecting the pressure change can be designed on the basis of the dynamic pressure principle.
To ensure a simple and at the same time versatile signal and data transmission, a data bus connects the signaling unit and/or the sensor units of the separate modular enclosure components with a central control and/or monitoring unit. The data bus used for this purpose is preferably an ASI bus.
To make the installation easy, an ASI flat-type cable module is provided, which connects the data bus through an opening in the modular enclosure component to the signaling and sensor unit.
To further increase the versatility of the unit, the pressure limiting values of the pressure sensor of each modular enclosure component can be set by the central control and monitoring unit by way of the data bus.
According to one particular embodiment of this invention, each modular enclosure component has means for setting the zero point and the two limiting values of its coordinated pressure sensor. This ensures that the operating point and the limiting values can be simply adjusted once the position and surface of the workpiece are determined to be perfect.
To ensure a compact design, the contact surfaces of the modular enclosure components and of the two enclosure end covers made to fit one another.
To reduce the production costs, the two enclosure end covers and especially the modular enclosure components have an identical design.
Additional advantages and features are revealed in the description of an embodiment of this invention as illustrated by the drawings.